Fisheries scientist Steven Hare coined the term "Pacific DecadalOscillation" (PDO) in 1996 while researching connections betweenAlaska salmon production cycles and Pacific climate. PDO has sincebeen described as a long-lived El Nino-like pattern of Pacificclimate variability because the two climate oscillations have similarspatial climate fingerprints, but very different temporal behavior.Two main characteristics distinguish PDO from El Nino/ SouthernOscillation (ENSO): first, 20th century PDO "events" persisted for20-to-30 years, while typical ENSO events persisted for 6 to 18months; second, the climatic fingerprints of the PDO are most visiblein the North Pacific/North American sector, while secondary signaturesexist in the tropics - the opposite is true for ENSO.Several independent studies find evidence for just two full PDO cyclesin the past century: "cool" PDO regimes prevailed from 1890-1924 andagain from 1947-1976 while"warm" PDO regimes dominated from 1925-1946and from 1977 through (at least) the mid-1990's. Shoshiro Minobe; hasshown that 20th century PDO fluctuations were most energetic in twogeneral periodicities, one from 15-to-25 years, and the other from50-to-70 years.